Aten asteroids are that sub-group of the Near-Earth Asteroid
(NEA) population with semimajor axes < 1 AU and aphelia
> 0.983 AU. As of 1998 May 24, the observed population is
502, 6% of which are Atens. This is a lower-limit because
search programs observe primarily around the opposition
point and, for a given size and albedo, Atens are generally
fainter than other NEAs at discovery. Thus the Aten
population is being seriously under-sampled in current
search programs.

If the Aten population is about 25% that of the Apollo
population, then their hazard potential is about half that
for the Apollos because the impact probability with the
Earth for an Aten is twice that for an Apollo (Bottke, {\it
et al.}, 1994, {\it Hazards due to Comets and Asteroids}, p.
337, T. Gehrels, ed.). Thus the under-sampling of this
population is significant in terms of the goals of the NEO
hazard search program.

According to Bowell and Muinonen ({\it Ibid.}, p. 149) it
would require 25 years to discover 33% of the Aten
population, with diameters larger than 0.5 km, if a 6,000 sq
deg/month area within 30 degrees of opposition were searched
to V < 22. This would increase to 83% by searching the
same area more broadly in longitude. Current surveys cover a
few thousand square degrees of sky per month to V \approx
20 and a few hundred square degrees to fainter limiting
magnitudes.

Preliminary results of our simulations show that a
space-based infrared system would discover (and
characterize) over 90% of Atens larger than 0.5 km in a
five-year period.

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